Historical overview of classification systems for common arterial trunk. (A) Collet and Edwards [3]. The left pulmonary artery (LPA) and right pulmonary artery (RPA) arise from the common arterial trunk (CAT) by interposition of a short pulmonary trunk (type 1), or the LPA and the RPA arise from the CAT with separate orifices, either with their orifices positioned close together (type 2) or widely spaced (type 3). Type 4, in which both pulmonary arteries (PAs) and the pulmonary trunk are absent and the pulmonary circulation is supplied by the aortopulmonary collateral circulation, is no longer considered the CAT. (B) Van Praagh and Van Praagh [4]. The ‘A’ in these subtypes refers to cases with ventricular septal defect (VSD) [5]. Cases without VSD (type B) are not included in the drawing. Type A1, in which the LPA and RPA arise from the CAT by interposition of a short pulmonary trunk, conforms to Collet and Edwards type 1. In type A2, the LPA and RPA arise from the CAT with separate orifices, either close together or widely spaced (combination of types 2 and 3 of Collet and Edwards). Type A3, in which 1 PA is lacking, refers to cases with a single PA supplying 1 lung and arteries arising from the ductus or collateral arteries usually supplying the other lung. Type A4 includes hearts with aortic, coarctation, atresia or absence of the aortic isthmus. The descending systemic circulation is supplied by a large persistently patent arterial duct. (C) In the modified van Praagh classification [45], a simplification was proposed by combining types A1 and A2 of Van Praagh and Van Praagh (i.e. combining types 1, 2 and 3 of Collet and Edwards), thus giving rise to a type A1–2 where the LPA and RPA arise from the CAT by interposition of a short pulmonary trunk or with separate orifices, either arising close together or widely spaced, without making this distinction. Types A3 and A4 conform to the original Van Praagh and Van Praagh classification. (D) Classification based on 2 subtypes: aortic versus pulmonary dominance [32, 46]. The aortic dominant type is characterized by adjacent or nearly adjacent PAs from the posterolateral aspect of the CAT, whereas in the pulmonary dominant type the distal systemic circulation is dependent on the patency of the arterial duct, as is encountered in cases of interruption of the aortic arch or coarctation. We endorse the latter classification as proposed by Russell et al. [46].